1. Field of the Invention
This invention relates to electronic circuit technology, and more particularly, to a dual mode transient recovery control method and system for fast transient recovery of the output of a DC (direct current) power output device, such as DC-DC converters.
2. Description of Related Art
DC-DC converters are an electronic circuit component that is nowadays widely used in many types of computer units and intelligent electronic devices. In operation, a DC-DC converter is capable of converting an input DC voltage having a higher amplitude (such as battery-supplied voltage) to an output DC voltage having a lower amplitude, such that the down-converted DC voltage is used to drive low-voltage IC (integrated circuit) chips, such as microprocessors, memory modules, digital signal processing chips, to name just a few. Nowadays, the present IC technology allows IC chips to operate with a system voltage as low as 0.8 V with a current of 200 A.
In practical applications, however, the operation of modern IC chips may provide serious load current variation in range of 20A to 200A due to the complexity thereof. Such serious load current variation may cause much serious output voltage transient response, such as over-shoot and under-shoot, to make the output voltage substantially deviating from the steady state value, which the output voltage should achieve. The output voltage may be provided with larger difference between the steady state value and the transient response by this deviation, thereby slowing down the transient response recovery.
One solution to the aforementioned problem is to employ a large decoupling capacitor that allows transient ripples to return to steady state more quickly. In practice, however, the solution with the large decoupling capacitor has two drawbacks: firstly, it is costly in price to purchase and thus would increase the overall manufacture cost of DC-DC converters; and secondly, due to the bulky size of the large capacitor, it would require a large circuit layout area for implementation of the DC-DC converters.
One solution to the aforementioned problem has been disclosed in U.S. Pat. No. 6,621,256 entitled “DC to DC converter method and circuitry”. This patent teaches a dual-mode switching control method which switches the DC-DC converter to operate in PWM mode under the condition of a heavy loading, and to operate in hysteretic mode under the condition of a light loading. Moreover, the performance of this dual-mode switching control method would be influenced by an internal inductance current, in such a manner that in PWM mode, it would exhibit a smaller ripple amplitude but a slower response; whereas in hysteretic mode, it would exhibit a faster response but a relatively larger ripple amplitude. This patent, however, is unable to solve the aforementioned problem.